1. Field of the Invention
This invention relates to a method of and apparatus for effecting spacial coordinate measurement, and more particularly to a coordinate measuring apparatus capable of measuring the roundness or the like of an object to be measured as well as its length and diameter.
2. Description of the Prior Art
One kind of apparatus for effecting coordinate measurement has been known in which an object placed on an object mounting table and a probe supported by a Z-spindle on the main body of the measuring apparatus are spatially moved relative to each other by a moving mechanism; the relative movement between the surface of the object to be measured and the probing tip of the probe is thereby detected; a signal representing the relative movement detected is processed by a data processing unit in a predetermined manner, and the contour, dimensions, etc. of the relevant object are thereby measured. This type of measuring apparatus is being used widely since they can measure the length, diameter, etc. of an object to be measured at high speed with a high degree of accuracy. There are two types of apparatus for use in coordinate measurement of this sort: a manual operation type in which the operator drives the moving mechanism by hand so that the probing tip of the probe is applied to or brought into contact with each measurement point on the object; and an automatic drive type in which the moving technique is driven by a drive source such as a motor under the control of a program.
However, since such a coordinate measurement measuring apparatus, including the manual and automatic operation types, make the probing tip of the probe and the object move in the direction of the composition on three orthogonal axes, that is, X-, Y- and Z-axes determined in accordance with the structure of the apparatus, it is designed to obtain a coordinate for each measurement point by, for instance, bringing the probing tip into contact with the inner peripheral surface of a hole at three points thereof to obtain the coordinate of each point when measuring the inside diameter of the hole, thereafter processing the coordinate data in a predetermined manner.
For this reason, it is impossible for the conventional apparatus for coordinate measurement to effect a measuring operation for identifying the roundness, the cylindricality or the like of an object since such an operation would require items of measurement data to be obtained continuous in the peripheral direction of the hole or shaft while the measuring operation of obtaining the length or diameter is being carried out. To identify the roundness or the like, it is necessary to remove the object from the object mounting table and reset it in a dedicated measuring apparatus, resulting in an extremely low degree of efficiency in the task of measuring. Also the accuracy of measurement is not good, since the conditions of measurement cannot be constantly maintained throughout the measurement process. In the case of the automatic drive type measuring apparatus, the work of removing the object from the mounting table or setting it thereon has to be carried out by the operator and this might affect the specific effectiveness of the automatic drive type.